1. Field of the Invention
The present invention relates to flow conditioners. Flow conditioners are used to create uniform flow field distributions to isolate fluid handling equipment and flow measurement devices from the effects of unstable or distorted flow fields entering the devices.
2. Background Art
Existing flow conditioners are typically either a thin perforated plate mounted perpendicular to the direction of flow, or a stack of tubes or rectangular channels aligned with the flow. Both of these existing flow conditioning techniques are effective at reducing an asymmetric flow field, but do so at the cost of a high pressure drop across the flow conditioner. These existing techniques also do not effectively reduce pulsation in the flow velocity or effectively reduce a high degree of vorticity in the flow field. To reduce the pressure drop across a flow conditioning device to a level that does not affect system operation, the blocking ratio should be low, for example, under 10%.
The classic Etolie swirl eliminator is an array of radial vanes parallel to the flow. The classic Etolie device has a low blocking ratio and effectively reduces large scale vortices in the flow. However, the classic Etolie device does not effectively reduce pulsation in the flow velocity, nor does the device effectively reduce an asymmetric flow field. Further, the classic Etolie device has an additional shortcoming in that it fails to remove the hysteresis in the transition between turbulent and laminar flow conditions or to reduce the length of straight conduit required for the flow conditions to develop fully.
Additional background information may be found in U.S. Pat. Nos. 6,186,179; 5,959,216; 6,145,544; 5,762,107; 5,529,093; and 4,841,781.
For the foregoing reasons, there is a need for an improved flow conditioner.
It is an object of the present invention to provide a low pressure drop flow conditioner with porous axial vanes.
In carrying out the present invention, a flow conditioner is provided. The flow conditioner comprises a body composed of an array of vanes or fins generally parallel to the direction of fluid flow to create a plurality of chambers. The vanes effectively reduce large scale vortices in the flow. To effectively reduce asymmetric flow, pores or perforations are made to the vane surfaces. These pores/perforations allow for pressure equalization between chambers and reduce drag.
At a more detailed level, the present invention comprehends arranging the vanes in a radial fashion, preferably with each vane extending radially from a central axis. The flow conditioner may have as few as three vanes. The porosity of the vanes preferably ranges from 35% to 70%. The perforations can be made in any shape, for example, circular, oval, diamond, rectangular or triangular and at any orientation with respect to the sheets composing the vane. The holes in the vane can be flush with the vane plate or have a small dimple where they were punched out of the sheet.
In preferred embodiments, to counter pulsation, a slight restriction in the cross-sectional area at the entrance and exit of the flow conditioner causes the volume between to be an acoustic choke. A contemplated implementation of this feature uses a circular plate at each end of the vane array. The circular plates are placed at the formed vertices of the vanes when the vanes are arranged in the radial fashion. More preferably, roughening the circular plates around their circumferences will increase the production of micro-vortices which cause a stable and repeatable trip between turbulent and laminar flow states. The circular plates (or rings) act as a turbulence trip and micro-vortex shedder, and may be solid, perforated, or annular.
For very low pressure drop applications, the circular plates can be as small as ⅙ the diameter of the conduit conducting the fluid. For other applications where a choke of 25% is acceptable, the diameter of the disk can be as large as xc2xd the diameter of the conduit.
Further, in carrying out the present invention, various flow conditioners are provided in combination with conduits to reduce vortices and asymmetric flow. The combinations employ various features described above.
The advantages associated with embodiments of the present invention are numerous. For example, preferred embodiments of the present invention effectively remove large scale vortices in the flow, reduce pulsation in the flow velocity, reduce asymmetric flow field, and increase the rate of flow development from turbulent flow to laminar flow.